02 Requirement Engineering

8/8/2019 02 Requirement Engineering

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Analyse User Requirements


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Performance Objectives

Outline fundaments of requirement

engineering

Analyse systems and models


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Software Engineering

Analyse User Requirements

Outline fundamentals of requirement

engineering


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Objectives

Enable you to

Why and what requirement engineering is for in

software system development

Organise system requirements for clients, usersand developers

Describe system validation

Discuss impact on system life cycle with changes in

requirements


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Requirements Engineering

Definition:

the process of establishing the services the system

should provide and the constraints under which it

must operate.

Why?

A systematic process is used to derive a definition

of the software system


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Problems

A failure to make clear separation between the

different levels of description

Why different level?Why different level?

This is useful as they communicateThis is useful as they communicate

information about the system to different typesinformation about the system to different types

of readerof reader


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Readers of the Requirements

Requirementdefinition

Client managers

System end-users

Client engineers

Contractor managers

System architects

System end-users

Client engineers

System architects

Software developers

Contractor managers

System architects

Software developers

Requirement

specification

Software

specification

Targeted at a managerial levelTargeted at a managerial level

Targeted at senior technicalTargeted at senior technical

staff & project managersstaff & project managers

ImplementationImplementation--orientedoriented

document for software engineersdocument for software engineers


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Levels of Requirement

Requirement definition

A statement of what services the system is

expected to provide and the constraints under

which it must operate Requirement specification

A structured document which sets out the system

services in detail

Software specification An abstract description of the software which is a

basis for design and implementation; add further

detail to the requirement specification


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System requirements should set out whatthe

system should do rather than howthis is done

A requirement may be

Functional system service or function

Non-functional constraints


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Example

Requirement definition

The software must provide a means of representing and accessing

external files created by other tools

Requirement specification

1. The user should be provided with facilities to define the type of

external files

2. Each external files type may have an associated tool which

may be applied to the file

3. Each external file may be represented as a specific icon on the

users display


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Requirements Engineering Process

A set of activities that lead to the

production of the requirements definition

and requirements specification.

4 principal stages:

Feasibility study

Requirements analysis

Requirements definition

Requirements specification


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The 4 principal stages

Feasibility study

inform the decision whether to go ahead with a more detailed

analysis

Requirements analysis

process of deriving the system requirements through

observation, discussions, task analysis, etc. Involve the

development of system models.

Requirements definition

activity of translating the information gathered into a set ofrequirements.

Requirements specification

sets out a detailed & precise description of the system

requirements


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Software requirements document

Includes requirements definition &requirements specification

Set out what the system should do without

specifying how it should be done Enable trace ability between these

requirements and the final system design

Complete, consistent, no conflict

May also include hardware and databaserequirements


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Requirements validation

Concerned with showing that the requirementsactually define the system that the customerwants

If inadequate, errors propagated to the systemdesign & implementation leads to expensivesystem modification at later stage to correct

problems.


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Several aspects which must be checked: Validity

Consistency

Completeness

Realism

Techniques: Prototyping

Regular Requirements review Checks for consistency, completeness, verifiability,

comprehensibility, traceability, adaptability.


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Requirements Evolution

Non-functional requirements are particularly affectedby changes in hardware technology

The requirements document should always be

updated so that it is an accurate reflection of the

system implementation

Initialunderstanding

of problem

Initialrequirements

Changedunderstanding

of problem

Changedrequirements

time


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Software Engineering

Analyze User Requirements

Analyze Systems and Models


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Objectives

Enable you to

Describe various approaches to analyzing current

systems and to elicit user requirements

Explain the role of system models Illustrate different types of system models

Explain the idea of a data dictionary

Produce a simple user requirement for a system


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Requirement Analysis Process

Requirement analysis is an iterative process

which involves

Requirements discovery

Requirements classification & organisation

Requirements prioritization & negotiation

Requirements documentation


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Requirement Analysis Process


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System models

One widely used technique to document systemspecification

Graphical representations that describe businessprocesses, the problem to be solved and the system

that is to be developed Bridge between the analysis and design processes

An abstraction of the system being studied rather thanan alternative representation of that system

Different types of system models are based on differentapproaches to abstraction


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Types ofSystem Models

A composition model

Shows how some entities in the system are composed of

other entities

A data-flow model

shows how data is processed at different stages

A classification model

Shows how entities have common characteristics

A stimulus-response model

Shows how the system reacts to internal and externalevents

An architectural model

Shows the principal sub-systems that make up a system


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Class Activity

Entity-Relation diagram

Data-Flow diagram

Class diagram

For each diagram above:

1. Describe briefly its purpose

2. State the notations used


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Composition Model

Software systems make use of large databaseof information.

Important to define logical form of the data

processed by the system. Using relational model with data structure

specified as a set of tables.

Technique: Entity-Relation (ER) Diagram


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Entity-Relation Diagram

A detailed, logical representation of the data

for an organization or for a business

application.

Sets out data entities and relations betweenthese entities. Entities can have attributes

which are atomic and not decomposed.


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Notations

Entity a business object about which you wantto collect data

Attribute a characteristic of an entity

Primary Key attribute(s) that assumes a uniquevalue for each entity instance

Relationship a meaningful association betweenentities with cardinality


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Example

Entity Employee Department

AttributesName, age, ic number,

gender, addressCode, Name

Identification Key IC number Code

Relationship

An EMPLOYEE is

assigned in one

DEPARTMENT

A DEPARTMENT has

one or more

EMPLOYEES


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Example - ERD

EMPLOYEE DEPAR TMENTASSIGN / HAS

name

age

ic number

gender address

code name


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Exercise

Produce an ER Diagram for the following scenario:

Students take courses in the university.

The courses are run by departments.

It is possible for a course to be run by more than onedepartment.

Each course consists of a number of units.

Lecturers teach the units, and in some circumstances morethan one lecturer will teach a unit.

Lecturers, of course teach more than one unit.

Since the introduction of modular courses, it is possible for

one unit to be included on more than one course.

A lecturer may be a course leader for a particular course.


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Answer

STUDENT DEPARTMENTASSIGN / HAS

name

age

Ic number

gender address

code name


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Data Flow Model

Models business processes of a system

Shows how data is processed by a system at

different stages

Technique: Data Flow Diagrams


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Data Flow Diagram

A technique used to show graphically

the flow of data through a business system and

the processes performed by the system.


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Processing step

Accepts input data & transforms it into output data

Data Flow

A path that the data takes in moving from one component ofthe system to another

Data store

where the system stores data because other processesneed to use them later

Entity

A person, department, organisation or other informationsystem that provides data to or receives output from system

Data name

Entity name

Notations

Process

Data store


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DFD Rules

Every Process must haveincoming & outgoing data flow

A process can have more thanone incoming or outgoing dataflow

A process can be connected to

any other symbols by usingdata flows

Process

Process

ProcessProcess


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A data flow must have a processsymbol on at least one end

A data store must be connected to aprocess with a data flow

Every data store must have at leastone incoming & one outgoing data

flow

ProcessProcess

Process


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Example - DFD

A Fast Food Ordering System

accept the order from Customerand

generate receipt forCustomer,

send order to the Kitchen, and

at the same time, update the related files in order to

generate useful reports to the Branch Manager


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Context Diagram

Customer

BranchManager

Kitchen

P

FastFoodOrdering

System

Order

Daily Reports

Receipt

Food Order


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Level 1 - Diagram 0

Customer

BranchManager

KitchenP1

ProcessCustomer

Order

Order

DailyReports

Receipt

Food Order

P2

UpdateItem Sold

File

P3

UpdateInventory

File

P4

GenerateDaily

Reports

D1 Item Sold File D2 Inventory File

Item Data Inventory Data

Sold Item List Inventory Data

Sales Information

Inventory Information


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Level 2 - Diagram 1

P1.1

AcceptOrder

Order

Receipt

Food Order

P1.3

PrintReports

P1.4

GenerateSold Item

List

P1.5

GenerateInventory

Sold Item List

P1.2

SendOrder ToKitchen

Order

OrderOrder

Order

Inventory Data


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Level 2 - Diagram 4

P4.1

EvaluateGathered

Information

Business Information

P4.2Generate

SalesStatistics

P4.3Produce

DailyReports

Inventory Data Sold Item List

Inventory Information Sales Information

Daily Reports


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Exercise

The level 1 diagram (shown in next slide) shows the

data movement in a traveling agency. Study the

diagram carefully and determine the errors in the

diagram

List the errors

Redraw the diagram and label the data flows so that it is

correct. You may have to cut down any replications and

duplications


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PrivateTravel

Agency

Tourist

CashPaymentTourist

1

CheckCredit

3

MakeReservation

2

DetermineDesired

Tour

D1 Tour Fee

D3 Travel Brochure

AirlineAgency

Tourist withCredit Card

D2 Credit History


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3

MakePayment

Answer

Private

TravelAgency

Tourist

4

CheckCredit

2

MakeReservation

1

DetermineDesired

Tour

D1 Tour FeeD3 Travel Brochure

AirlineAgency

D2 Credit History


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Classification Model

Shows how entities have common

characteristics

Called Object models

Shows how entities in the system may be

classified and composed of other entities.

They model classes of objects representing

real-world entities.


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Object Class/Inheritance

An object class

an abstraction over a set of objects which identifies

common attributes and the services or operations

which are provided by each object.

Class name

Attributes

Services

Notations

An object class is divided into three parts:

Class namename of the object class

Attributeslists the attributes of that object

class.

Services - the operations associated with the

object.


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Taxonomy

These classes of object are then organized

into a taxonomy.

a classification scheme which shows how an object

class is related to other classes through commonattributes and services.

To display this taxonomy,

classes are organized into an inheritance or class

hierarchy

the most general object classes at thetop of class hierarchy.

More specialized objects inherit their attributes and

services. These specialized objects may have their

own attributes and services.


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Example

Figure

Location

Line color

ClosedF

igureArea

Fill color

OpenF

igureLength

LineEllipse

Eccentricity

Polygon

No. of sides

Circle

Radius

Rectangle

Length

Width

Triangle

Base

Height

x

y


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Data Dictionaries

Also known as Catalog or Repository

Stores the metadata (data about data) of a businessinformation system

A list of names used by the system arranged

alphabetically. Stores information about business entities and their

relationships with one another (business rules),attributes of entities, primary and foreign keys,validation rules and triggers.


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Example

Name Description Type Date

has_labels 1:N relation between entities of type

Node or Link and entities of type Label

Relation 5.10.93

Label Holds structured or unstructured

information about nodes or links. Labels

can be text or can be an icon.

Entity 8.12.93

Link Represents a relation between design

entities represented as nodes. Links are

typed and may be named.

Relation 8.12.93

name (label) Each label has a name which identifies

the type of label. The name must be

unique within the set of label types used

in a design.

Attribute 8.12.93

name (node) Each node has a name which must be

unique within a design. The name may be

up to 64 characters long.

Attribute 15.11.93

Date post:	10-Apr-2018
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02 Requirement Engineering

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